Methylene chloride solution of polyethylene terephthalate



Sept. 10, 1968 L D ET AL 3,401,140

METHYLENE CHLORIDE SOLUTION OF POLYETHYLENE TEREPHTHALATE Original FiledOct. 22, 1965 P0 LYNER CONCENTRATION A TEMP. "C

INVENTORS HERBERT BLADES JAMES RUSHTON WHITE ATTORNEY United StatesPatentOflice 3,401,140 Patented Sept. 10, 1968 METHYLENE CHLORIDESOLUTION ()F g I v POLYETHYLENE TEREPHTHALATE Herbert Blades,Wilmington, Del., and James R. White, ChapelHill, N.C., assignors 'to E.L du Pont de Nemolirs 'and Company, Wilmington, Del., a corporation ofDelaware Continuation of application Ser. No..501,610, Oct. 22, 1965.This application Mar. 8, 1967, Ser. No. 633,324

Claims. (Cl. 260-33.8),

ABSTRACT on THE DrscLosuRi: Polyethylene terephthalate solutions inmethylene chloride can be prepared'that are useful for the preparationof fibers and-other shaped articles.

10, 1959 (both now abandoned), and SerL No. 736,337,

filed'May 19, 1958, (now abandoned), which are in turncontinuations-in-part of application Ser. No. 665,099, filed June 11,1967 (also now abandoned). i i

The polymer solutions of this invention are composed of 10 to 80 percentby weight of polyethylene terephthalate dissolved in an organicsolventmedium, at least about 75% by Weight of which solvent medium ismethylene chloride. Said solutions are maintained at a temperaturebetween 170 C. and 260 C. and under at least autogenous pressure. a: i

The polymer solutions described above are useful for the preparation offibers or other shaped articles. As .Will be further understood from thediscussion hereinafter, such articles may comprise ultramicrocellular orplexifilamentary structures as. described in detail: in U.S. Patent3,227,664 and U8. Patent No. 3,081,519, respectively.

That methylene chloride can serve as an outstand ingly useful solventfor polyethylene terephathalate, under elevated temperature and pressureconditions, is surprising since heretofore polyethylene terephthalatehas been regarded as insoluble or, at best, only very slightly solublein low-boiling organic liquids, particularly ones that areunobjectionable for commercial fiber spinning processes.

The polymer solutions of this invention may be maintained, under thetemperature and pressure conditions indicated, in a pressure vessel ofany suitable type.

Polyethylene terephthalate polymer suitable for forming the solutions ofthis invention should be of at least film-forming molecular weight;i.e., it is a high polymer material.

The term polyethylene terephthalate as used herein is intended to coverhomopolymers as well as copolymers, such as polyethyleneterephthalate/isophthalate in varying proportions by weight, butpreferably at least 50% of ethylene terephthalate units. Suchcopolymers, while not necessarily preferred, also form useful spinningsolutions in methylene chloride. It is well known that the copolymersare usually more soluble in a given organic solvent, but increasingdegrees of copolymerization modify certain desirable properties ofpolyethylene terephth'alate homopolymer. The surprising feature of thisinvention is that the homopolymer is completely soluble over a broadrange of temperature and composition.

For certain purposes, the polymer solutions will preferably contain 20to 80% by weight of polyethylene terephthalate. Preferably at least 79%by weight of the organic solvent medium will be methylene chloride. Theremainder may 'be a perhaloalkane, e.g., a fluorinated orchlorofiuorinated alkane of 1 to 2 carbons.

FIGURE 1 is a portion of the concentration-temperature phase diagram forpolyethylene terephthalate/rnethylene chloride binary systems. Polymerconcentration for the ordinate is expressed as weight percent of polymerbased on the whole solution, and concentration as used hereinafter isunderstood to have this meaning.

With reference to FIGURE 1, the line AGLND is the melting curve atautogenous pressure. The meaning of melting curve is clear from thefollowing. If solid polyerly a band deviating about :5%

mer and solvent are mixed at a specified concentration level and heatedunder autogeneous pressure, solid and solution phases are in equilibriumfor all temperatures lower than that on the melting curve for thatconcentration. At higher temperatures, a single-phase solution results.Because the melting point varies slightly with polymer molecular weightand because of experimental difficulties in determining precisely thetemperature at which complete solubility occurs, the melting curve ismore propin concentration from line AGLND.

Substantial degrees of undercooling of the solutions are possible sothat the freezing curve (as observed Within a reasonable time scale)comes at considerably lower temperatures than the melting curve. Line AErepresents the lower practical limit of temperatures for maintainingonephase solutions, which limit is also molecular weight dependent. Suchundercooled solutions-even through metastable-perform satisfactorily.

Curve BHJC is the single-phase boundary for autogenous pressures.Between the belting curve and this singlephase boundary, the solution isone liquid phase. At tem peratures greater than those indicated by CurveBHJC, two liquid phases form unless sufiicient superautogenous pressureis applied to prevent phase separation. As is readily understood, theprecise location of curve BHJ C is also slightly affected by themolecular weight of the polymer employed. Pressures substantially inexcess of autogenous are, of course, frequently employed at temperatureslower than those represented on the single-phase boundary.

As disclosed in our copending application Ser. No. 354,192, the areaABCDE of FIGURE 1 represents conditions which lead to microcellularstructures, and area FHJKM is the preferred operating area. Solutionscorresponding to the area above and to the right of curve BHJ C can leadto the plexifilamentary structures of US. Patent No. 3,081,519.

It is not necessary that pure methylene chloride be used as solventmedium, as long as at least about by weight is methylene chloride. Theremainder can be any of a number of soluble, organic additives.

When super-autogenous pressures are desired, they may readily beobtained by dissolving a lower boiling additive. Although any solublelow-boiling material is suitable, the preferred materials are thosewhich are super-critical at temperatures above the polymer meltingpoint. Useful additives include N CO He, He methane, ethane, propylene,ethylene, certain fluorinated and/or chlorinated methanes and ethanes,and equivalents.

A solvent medium composed of methylene chloride and a soluble additiveshould be an activating liquid as defined in application Ser. No.354,192. Specifically, the solvent medium employed: (1) should have anormal boiling point at least 25 C. less than the polymer melting point;(2) should be substantially unreactive with the polymer during mixingand extrusion; (3) should be a solvent for the polymer under theconditions of temperature, concentration, and pressure suitable for thesolutions of this invention; (4) should dissolve less than about 1% ofthe polymer at or below its boiling point; and (5) should form asolution which will undergo rapid vaporization upon extrusion to form anon-gel polymer phase. Thus, suitable additives need not necessarily fitrequirements 1 to 5 above, but they must, of course, be soluble inpolyethylene terephthalate/methylene chloride solutions.

In general, the use of additives to the solvent medium shifts themelting curve AGLND to higher temperatures and the single-phase boundaryBHJC to lower temperatures. As can be seen in FIGURE 1, this narrows theconcentration-temperature range in which single-phase solutions arestable at autogenous pressures, and still higher pressures are morefrequently required.

Inert, insoluble, solid particulate materials can be dispersedthroughout the solutions of this invention. One method for providing alarge number of bubble nuclei at the instant of extrusion is toincorporate solid nucleating agents in the polymer solution.

This invention is further illustrated by the following examples.

EXAMPLE I 400 grams of polyethylene terephthalate polymer (relativeviscosity=50, vacuum oven dried at 120 C. for 24 hours) and 250 ml. ofmethylene chloride (dried over calcium hydride) were charged to a 1liter pressure vessel, 70 grams of dichlorodifluoromethane (e.g., Freon12) was added and the vessel was closed, heated to 210 C. while turningend over end, held at 210 for ten minutes, cooled to 191 C., held 15minutes, positioned vertically, and pressured with 800 p.s.i. nitrogen.The solution was spun at a velocity of approximately 3,000 y.p.m. (2700m./min.) through a mil (0.51 mm.) diameter hole 28 mils (0.71 mm.) longand the fiber collected in a barrel. After heating for 15 minutes at 100C. to expel residual solvent and realize maximum inflation, themicrocellular product is a continuous, smooth, turgid fiber,density=0.023 g./cc., tenacity=0.57 g.p.d., elongation=39%, modulus=2g.p.d. and denier=l,000 (properties determined on boiled off filaments),relative viscosity of fiber=29.2. The yarn is stable to a 20 minuteboil-off, elongating only 1.6%. The strand contains about 10 cells/ cc.The average cell diameter is 36 microns, the wall thickness 0.1 micron,and the polymer in the cell walls exhibits planar orientation to within10 degrees. The cell walls exist in polyhedral configuration withsubstantially no polymeric material present other than that comprisingthe polyhedral cellular structure.

EXAMPLE II A 2-inch (5.08 cm.) diameter Hartig extruder is modified bythe addition of a 2-section barrel extension. The screw has a 15/1 L/Dfeed section followed by a 4.5/1 L/D metering section and a 9/1 L/Dtorpedo mixing section. It is driven by a HP motor with a Dynamaticadjustable speed coupling. The end of the extruder is fitted with anorifice 0.020 inch (0.508 mm.) in diameter with a 0.040 inch (1.016 mm.)land (preceded by a 100 mesh screen). The barrel is heated by means ofeight individually controlled heaters.

A 21 weight percent solution of unsymmetrical trichlorotrifiuoroethanein methylene chloride is fed from a graduated reservoir through aheating coil at 80 C. to an injection probe protruding into the flowingpolymer stream by means of a Hills-McCanna Co., McCannameter diaphragmpump, model MA8'88-D. The methylene chloride solution enters the polymerstream at the transition between the metering and the mixing sections.

A microcellular fiber is extruded under the following conditions.

Polyethylene terephthalate (previously vacuum dried at 100 C.) 41.7lb./hr. (18.9 kg./hr.). 1,1,2 trichloro 1,2,2 trifiuoroethane 3.35lb./hr. (1.52 kg./hr.). Methylene chloride 12.7 lb./hr. (5.77 kg./hr.).Die melt temperature 225 C. Die pressure 800-900 p.s.i. (56.3-63.3

kg./cm. Relative viscosity: 7

Molding pellets 35. Fiber 28.

The yarn produced by this procedure was smooth surfaced and pneumaticand was composed of closed cells approximately 10-20 microns indiameter. The apparent density of the yarn is 0.04 g./cc.

EXAMPLE III A 300 ml. pressure vessel is charged with 90 g. ofpolyethylene terephthalate (relative viscosity of 49), 90 m1. ofmethylene chloride, and 20 ml. of sym-dichlorotetrailuoroethane, heatedto a temperature of 205 C. and extruded under a total pressure of 840p.s.i.g. (59.1 kg./ cm. of nitrogen. The 0.012 (0.30 mm.) diameterorifice is preceded by a 200 mesh screen located 1" (2.54 cm.) away. Asmight be predicted from consideration of FIG- URE 1, the initial productis a microcellular closed cell filament. However, after a few secondsoperation, the product produced is a plexifilamentary strand, due to theoperation of a preflashing mechanism at the up-stream screen.

What is claimed is:

1. A polymer solution composed of 10 to 80 percent by weight ofpolyethylene terephthalate dissolved in an organic solvent mediumconsisting essentially of 100% methylene chloride and 0 to 25% of aperhaloalkane which at or below its boiling point is a nonsolvent forsaid polyethylene terephthalate maintained at a temperature between 170C. and 260 C. and under at least autogenous pressure.

2. A pressure vessel containing the polymer solution according to claim1.

3. The polymer solution of claim 1 wherein said solvent medium consistsessentially of methylene chloride.

4. The polymer solution of claim 1 wherein said solvent medium containsat least 79% by weight of methylene chloride.

5. The polymer solution of claim 1 wherein said polyethyleneterephthalate is a homopolymer.

6. The polymer solution of claim 1 wherein said solvent medium containsa member selected from the group consisting ofunsym-trichlorotrifluoroethane, dichlorodifiuoromethane andsym-dichlorotetrafluoroethane.

7. The polymer solution of claim 1 containing 20 to 80% by weight ofpolyethylene terephthalate.

8. A method for producing a spinning solution of polyethyleneterephthalate in an organic solvent medium comprising introducing into areceptacle (A) polyethylene terephthalate and (B) a solvent mediumconsisting essentially of 75 to methylene chloride and 0 to 25 of aperhaloalkane which at or below its boiling point is a nonsolvent forpolyethylene terephthalate, the polyethylene terephthalate comprisingbetween 10 and 80% by weight of the combination of A and B, closing thereceptacle and heating the mixture therein with agitation to atemperature between C. and 260 C. under at least autogenous pressure toobtain a homogeneous solution.

9. The process of claim 8 wherein the solvent medium is methylenechloride.

5 6 10. The process of claim 8 wherein the solvent medium FOREIGNPATENTS includes a member selected from the group consisting of 645,0321O/1950 Great Britain. unsym -trich1or0trifluoroethane,dichlorodifluoromethane 7 5 7 /1958 Great Britain andsym-dlchlorotetrafiuoroethane. 5 OTHER REFERENCES Ref r nc s Cit dShepherd: Aerosols; Science and Technology, Inter- UNITED 50161166 Pub.,pp.

2,743,250 4/1956 Sweet 260--33-8 JULIUS FROME, Primary Examiner.

